Tunnel kiln and method of operation



May 18, 1965 D. P. SHELLEY TUNNEL KILN AND METHOD OF OPERATION 5Sheets-Sheet 1 Filed Oct. 4, 1963 g j @Q Ch n-"file OM, i MN i OM, Inwwwnnluflr NW NW TLT NM 07/ ,u M 5Q livv lm DONALD P; BSHELLEY xAllorneij May 18, 1965 D. P. SHELLEY TUNNEL KILN AND METHOD OF OPERATION5 Sheets-Sheet 2 Filed Oct. 4, 1965 A a a M \w F o 3 i m L .A U 1i 2fil. v n 0 L \W O 2 w ,r o \3 I l a 3 2 M I nuenlor A ltomey s May 18,1965 D. P. SHELLEY 3,184,224

TUNNEL KILN AND METHOD OF OPERATION Filed Oct. 4, 1963 5 Sheets-Sheet 3I ;nvenlor DONALD P. SHELLEY Attorney 5 May 18, 1965 D. P. SHELLEYTUNNEL KILN AND METHOD OF OPERATION 5 Sheets-Sheet 4 Filed Oct. 4, 1963Inventor DONALD P. SHELLEY By 1 I z Aiforney;

y 13, 1955 D. P. SHELLEY 3,184,224

TUNNEL KILN AND METHOD OF OPERATION Filed 001;. 4, 1963 I 5 Sheets-Sheet s M 7 w 7 I Q g'g g r\, l 0 Q N L O \l g E L E Q I 4 P, m Q s 6 1 xQ) Q K! Q Q R?- -g Q 3 D Inventor DONALD P. SHELLEY By/f r mad AttorneyUnited States Patent 3,184,224 TUNNEL KILN AND METHOD OF OPERATIGNDonald P. Shelley, Ravenswood, Airdale Road, Stone, England Filed Oct.4, 1963, Ser. No. 313,861 Claims priority, application Great Britain,Oct. 9, 1962,

13 Claims. (Cl. 26328) This invention relates to kilns, furnaces andother heat treatment chambers or tunnels, which for the sake ofconvenience in description will be broadly referred to as kilns. Theinvention is particularly applicable to the firing of ceramic ware suchas tiles, table ware and so forth.

Present trends towards high-speed firing create difiiculties ineffecting the travel of the goods through the kiln. Typical arrangementsnow available include the provision of run-ways along the kiln floorover which batts carrying the goods are pushed. The batts usually takethe form of flat slabs of refractory material.

The object of this invention is to provide a more smooth and easy way ofcarrying the goods through the kiln.

The invention includes both a method of doing this and an apparatus forcarrying the method into effect.

The invention consists in creating a film or cushion of air over thesurface of the kiln hearth or floor, and sup porting the goods on thefilm or cushion while at the same time effecting their propulsionthrough the kiln.

The invention also consists in a kiln having a hearth which is providedwith perforations, means being provided for blowing air under pressureupwards through the perforations, and means for feeding goods into thekiln on the hearth, whereby the air blown upwards through theperforations will impinge on the underside of the goods, and so supportthe goods while they travel through the kiln.

Constructional forms of the invention will now be described withreference to the accompanying drawings in which:

FIGURE 1 is a longitudinal section, partly broken away, through a tunnelkiln comprising a number of separate units.

FIGURE 2 is a sectional part plan on line CC of FIGURE 1.

FIGULRES 1 and 2 are drawn to a smaller scale than the other views.

FIGURE 3 is a longitudinal section through one of the units which makeup the complete kiln.

FIGURE 4 is a diagram showing two streams of goods moving in oppositedirections through the kiln.

FIGURE 5 is a transverse section on lines AA of FIGURES 1 and 2.

FIGURE 6 is a transverse section on lines BB of FIGURES l and 2.

FIGURE 7 is a cross-section through the kiln hearth illustrating amodified arrangement and FIGURE 8 is a perspective view showing an airdeflector member used in the arrangement of FIGURE 7.

FIGURE 9 is a similar view to FIGURE 7 illustrating another modifiedarrangement.

The kiln comprises a refractory structure It defining an internal cavity11 extending lengthwise of the kiln. The refractory structure isenclosed in insulating walls 12. The kiln is of considerable length andis built up from a number of separate units, one of which is shownseparately in FIGURE 3. Each unit is supported on four pillars -13 eachprovided with a runner Wheel or roller 14 at its base riding upon a railtrack 15.

If any one unit should become faulty for any reason it can therefore belifted out of the kiln as soon as its neighbouring units have beenslightly opened out, and a reserve unit, which can easily be maintainedheated up in readiness, can he quickly inserted.

Heating elements 16, for example gas or oil burners or electricradiants, are mounted underneath the hearth I? of the kiln in a heatingchamber 11, and the hearth has perforations :18 which allow the heat torise up among the goods. Perforated baflles 19 at each side of thehearth allow heat to circulate among the goods from above. The hearth issupported on pillars 20 which are spaced apart from each other so as toallow free air circulation from the elements 16. As shown the hearth isformed in two parts, indicated as 17' and I7 and these each extendlengthwise through the kiln and are sloped to opposite gradients, seeespecially FIGURE 4; in this figure, however, the gradients areexaggerated; in practice they are probably not steeper than 1 in 500.Thus in the kiln illustrated the goods move in two streams, side byside, the direction of flow being down the gradient in each case.

In some cases the goods are supported on batts 22 the goods in this casebeing indicated as cups or similar articles 23. FIGURE 7 shows amodification in which the batts are omitted and the goods themselves arein the form of ilat articles such as til-es 24, which can move alongwithout the need for supporting b-atts. Where batts are used, seeespecially FIGURE 2, upstanding guide members 2 5 of refractory materialare cemented in pockets in the hearth to prevent sideways movement ofthe advancing batts. Where batts are not used, the tiles 24 or otherarticles .are centered by means of air deflector members 26 fitted atboth sides of each stream of tiles and designed to direct jets of airinwards against the sides of the tiles, the deflector members 26 beingformed with gaps 27, FIGURE 8, by Way of which air can escape fromunderneath the tiles. These jets of air are derived from a closedcircuit of air which is blown through .a duct '30 in each unit of thekiln by means of a fan 31, the duct being an expander, wideningdownwardly to its lower end where it delivers the air underneath thehearth 17. This air rises up through the perforations 18 in the hearthand supports the batts 22 (or tiles 24 as the case may he) on a film orcushion of .air over the hearth. The travel of the goods through thekiln on this film or cushion is initiated by means of an endlessconveyor 32 which may consist of wire bands, the conveyor being drivenat a suitable speed so that it feeds the batts or tiles successivelyinto the kiln. Each batt or tile pushes against the preceding one andthis action, in conjunction with the slight gradient to assist the flow,is sufficient to effect propulsion. There is a similar endless conveyor32 at the other end of the kiln operating at the same speed to removethe goods. Each stream of goods has two conveyors, one feeding into thehigher end of the stream, and one removing at the lower end. The fans 31are each carried by a frame structure .35 on the top of each unit of thekiln, the frame structure carrying a driving motor 36, which isconnected through pulleys 37, 38 and a belt 39 with a hollow drivingshaft 46 carried in bearings 41, 42. The frame 35 also carries arefractory plug 43 inserted into the top of the kiln unit to enable thefan assembly to be withdrawn when necessary for inspect-ion or servicepurposes. It is desirable to provide for cooling the bearings of the fanand its driving gear, for which purpose cooling water is allowed tocirculate through a tube 44 passing centrally through the driving shaft40, the water entering by way of one of a pair of connections 45, 46 andleaving by the other. flowing down the tube 44 and back upwards againbetween the tube 44 and the hollow shaft 40. Further cooling water isintroduced into a jacket 47 for cooling the bottom bearing. In additionthe shaft 40 carries a spinner 48 above the top of the plug 43 whichassists in the dissipation of heat arising.

Each unit of the kiln is amount of heat transfer from one zone or unitto its neighbours; To assistin this, each unit includes a b-afile member50 depending downwards'into the main'internal cavity 11, at right anglesto the direction of flow, and the bottom of the bafile is arranged atsuch .a level that'the goods the kiln hearth 17. r

-It will be seen that each unit or zone of the kiln has its own fan unitwhich delivers hot air to the hot air chamher under the hearth where theheating elements '16 are situated, so that a continuous circulation ofhot air is thus promoted by drawing the hot air from the top of the kilnand introducing it at the bottom, and the recirculating air thuspromotes forced convection for both heating and cooling. Each z-oneforms in eflect a heat exchanger, removing heat from fired goods movingin one direction and heating up goods moving in the opposite direction.a g

In the arrangements illustrated therheating means is separate from thecirculating air blown through the kiln by the fans, but it would bepossible to pre-heat the circulating air, for example by means externalto the kiln,

so that the circulating air itself constituted the heating medium.Provision may be made in any case for introducing fresh air or allowingsome of the circulating air to be drawn 01f, in each separate unit.

FIGURE 9 shows a modification in which a centralising effect is obtained:on batts travelling through the kiln by shaping the undersides of thebattsZZ, as shown at 22, and the upper surface of the hearth 17, with ashallow V-shaped, concavo-convex or trough-like relationship in theircontours. v

Although only two streams of goods have been shown in the drawings, itwill be evident that a kiln can be de-' signed to accommodate a largernumber of streams, and these may be in one or more layers.

1 claim: v

1. A method of heating workpieces of ceramic, jorjlike material, in akiln having a hearth, comprisingthe steps of creating a film of heated'air under pressure over, the

surface of the hearth to support the workpieces slightlyabove'thehearth, continuously feeding the wo r kpieces on to the hearthfrom both ends of the kiln in plural streams that, are oifset from eachother, pushing the pieces through the furnace by placing each piece incontact with the pre ceding piece, so that while supported by thepressurized air the work-pieces are propelled in opposite directions 1arranged to form a self-contained heating zone, asvfa-r as possible,with the minimum batts, and continuously feeding the batts on to, thehearth firom both ends of the kiln in plural streams that are offsetfrom each other, pushing the batts through the furnace by placing eachbatt in contact with the preceding batt,

so that while supportedby the pressurized air the batts are propelled bythe" incoming batts pushing forward those already in the kiln.

4.A method ofv heating workpieces of ceramic, or like material, in akiln having a hearth, comprising the steps of creating a film of heatedair under pressure over the surface of the hearth to support theworkpieces slightly above the hearth, placing the workpieces onsupporting propelled in opposite directions from each end of the lengthand through said chamber, means for creating supporting cushions of hotgas under said workpieces, means longitudinally dividing the chamberinto a series of zones, and means for dilferentially heating saidcushions of hot gas in the series of zones so astto progressively heatthe workpieces in each stream to peak temperature and then progressivelycool the workpieces as they move through the chamber.

6. Apparatus for heat treating workpieces of ceramic,

or like material, comprising a kiln, a chamber in the kiln,

a plurality of batts each for supporting at least one Workpiece, meansfor propelling at least two continuous streams of contacting battsin'opposite directions along the length and through said chamber, meansfor creating supporting cushions of hot gas under'said batts, meanslongitudinally dividing the chamber into a series of zones, and meansfor difierentially heating said cushions of hot gas in the series ofzones so as to progressively heatthe batts and supported workpieces ineach stream to peak temperature and then progressively cool them as theymove through;

thetchamber, V

7. Apparatus for heat treating workpieces of ceramic, or like material,comprising a kiln,a tunnel-like chamber extending through the kiln,bafiles dividing the. chamber longitudinally'into separate zones tominimize heat, trans- V for between adjacent zones, a pair of hearths ineach of said zones dividing each zone transversely to the length of saidchamber, apertures in said hearths, means for propelling at leasttwocontinuous streams of contacting workpieces through the kiln in oppositeends of the chamber, and means for projecting hot gas through saidhearth apertures to create supporting cushions 'of hot gas below thestreams ofworkpieces, said meansforiprojecting the that are offset fromeach other, pushing the pieces-through;

the furnace by placing each piece in contact with the preceding piece,so that while. supported'by the pressurized air the workpieces arepropelled in oppos te directions from each end ofthe hearth'by'theincoming workpieces pushing forward those already in the kiln,circulating said heated air upwardlyglaterahy and downwardly to againcontact both streams of workpieces, and utilizing gravity 2 to assistinpropelling the workpieces by providingthe hearth with a downwardgradient.

- 3. method of heating workpieces of ceramic, orlike material, in a kilnhaving a hearth, comprising the steps ofv creating a film of heatedairunder pressure over the surface of the hearth to support the workpiecesslightly above the hearth, placing the workpieees on supporting hot gasincluding means for progressively increasing temperature up to a peakand then progressively decreasing temperature from said peak in both theoppositely moving streams as said workpieces move through the kiln.

'8. Apparatus according to claim 5, wherein means for circulating thehot gas is provided in each of said zonesso 9. A kiln as claimedin'claim 8, wherein [said means for-circulating the hot gas in each:zone includes a fan disposed in the upper part of said chamber andadapted to be above said workpieces, a passageway in thelwall' of thekiln communicating the spacejoccupie'd by said fan with the space in thechamber adapted to be under said work- 'pieces said fans being soarranged as to direct hot gas in each zone through said passageway on toworkpieces in both said streams so that incoming pieces to the zone areadapted to be heated and workpieces outgoing from a zone are adapted tobe cooled by the same gas.

1 10. Apparatus as claimed in claim 9, wherein each said fan is arrangedto receive both gas which has passed over incoming workpieces to heatthem and gas which has passed over outgoing workpieces to cool them.

11. Apparatus as claimed in claim 5, wherein means are provided toenable workpieces being cooled in a zone to exchange heat directly toworkpieces being heated in the same zone.

12. Apparatus according to claim 7, wherein said pair of hearths in eachzone is provided with oppositely disposed gradients facilitatingpropulsion of both streams of workpieces.

13. Apparatus according to claim 10, wherein said means longitudinallydividing the chamber includes a separate furnace unit forming each ofsaid zones of the kiln,

and means for removably fitting together the separate units to form saidtunnel-like chamber.

References Cited by the Examiner UNITED STATES PATENTS 756,600 4/04Dodge 2633 X 1,829,710 10/31 Dauch et al. 263-28 1,867,772 7/32 Smalley263-28 1,948,173 2/34 Hagan 2633 X 2,215,581 9/40 Fackt 263-28 2,311,9082/44 Vranken 263-26 X 2,538,972 1/51 Magnani 30229 2,749,109 6/56 Maud263-6 3,071,356 1/63 Duffy 2636 CHARLES SUKALO, Primary Examiner. JOHNJ. CAMBY, Examiner.

3. A METHOD OF HEATING WORKPIECES OF CERAMIC, OR LIKE MATERIAL, IN AKILN HAVING A HEARTH, COMPRISING THE STEPS OF CREATING A FILM OF HEATEDAIR UNDER PRESSURE OVER THE SURFACE OF THE HEARTH TO SUPPORT THEWORKPIECES SLIGHTLY ABOVE THE HEARTH, PLACING THE WORKPIECES ONSUPPORTING BATTS, AND CONTINUOUSLY FEEDING THE BATTS ON TO THE HEARTHFROM BOTH ENDS TO THE KILN IN PLURAL STREAMS, THAT ARE OFFSET FROM EACHOTHER, PUSHING THE BATTS THROUGH THE FURNACE BY PLACING EACH BATT INCONTACT WITH THE PRECEDING BATT, SO THAT WHILE SUPPORTED BY THEPRESSURIZED AIR THE BATTS ARE PROPELLED BY THE INCOMING BATTS PUSHINGFORWARD THOSE ALREADY IN THE KILN.